Node.js is an open-source, cross-platform Javascript run-time environment that executes Javascript code outside the browser. Historically, Javascript was used primarily for client-side scripting, in which scripts written in JavaScript are embedded in a webpage's HTML and run client-side by a JavaScript engine in the user's web browser. Nowadays, Node.js represents a "JavaScript everywhere" paradigm, unifying web application development around a single programming language, rather than different languages for server side and client side scripts.